Meiko and Hozumi were once the best of friends as children but an incident at the age of nine causes a rift between them. Now middle schoolers, Hozumi continues to ignore her but Meiko is still hung up over their estrangement and finds herself unable to move on from the event. One day, Meiko encounters a young boy who looks strikingly like Hozumi. Is he an illusion? A ghost? Or something else entirely?A time paradox story about youth, juvenile delinquency, and changing a bad future.
The manga focuses on a certain unnamed character who appears throughout the story of A Certain Scientific Railgun and A Certain Magical Index, and whose name is revealed in this story set at Tokiwadai Middle School.